Tetrafluoroethylene/fluoroalkoxy trifluoroethylene copolymer composition

ABSTRACT

A tetrafluoroethylene/fluoroalkoxy trifluoroethylene copolymer (PFA) composition which has finer spherulite diameters compared to a conventional PFA is provided, so as to give fabricated articles having excellent surface smoothness, and which are free from problems, such as process contamination and the like, caused by leaching. This effect is obtained by incorporating into the composition prior to fabrication a polytetrafluoroethylene having a crystallization temperature of at least 305° C. and a heat of crystallization of at least 50 J/g.

This is a division of application Ser. No. 08/264,122, filed Jun. 22,1994 now U.S. Pat. No. 5,473,018.

FIELD OF THE INVENTION

The present invention relates to a tetrafluoroethylene/fluoroalkoxytrifluoroethylene copolymer composition which gives a melt extrudedproduct having excellent surface smoothness.

BACKGROUND OF THE INVENTION

Melt formable tetrafluoroethylene/fluoroalkoxy trifluoroethylenecopolymers (known by the acronym PFA) have excellent characteristics inheat resistance, chemical resistance, and the like, and are used toobtain bottles and tubes by melt extrusion, which find use in containersfor high-purity chemicals used in semiconductor manufacture or tubingfor transporting liquid chemicals or ultra-pure water.

The problem has arisen in semiconductor-related applications, thatarticles extruded from PFA do not have smooth surfaces, so thatcontaminants in the liquid chemicals used in these applications tend toadhere to the surface, and are difficult to remove even upon rinsing.

The reason the surfaces of the PFA-extruded products are not smooth isthat coarse spherulites, reaching diameters of 20-150 micrometer (μm),are generated during the crystallization of PFA, with their spheruliteborder regions generating deep grooves on the surface of the moldedproducts. It is generally known that the size of a spherulite can bemade smaller by increasing the number of spherulite nuclei. A variety ofinorganic or organic crystallization nucleating agents have been addedto crystalline resins for this purpose. Nucleating agents for renderingfiner spherulites in fluororesins have also been proposed, which includemetal sulfate salts for polychlorotrifluoroethylene (Japanese PatentApplication Publication Kokai 49-5153) and alkali metal salts forpolyvinylidene fluoride (Japanese Patent Application Publication49-17015) However, in semiconductor manufacturing process-relatedapplications which require particularly high purity liquid chemicals orultra-pure water, metal salt nucleating agents will leach out, causingcontamination in the process steps and adversely affecting PFA'schemical resistance and minimal contamination advantages.

SUMMARY OF THE INVENTION

Study by the present inventors has led to the finding that incorporatingin a PFA a small amount of a specific polytetrafluoroethylene (PTFE) canrender the spherulites finer to substantially improve the surfacesmoothness of the extruded products without adversely affecting thecharacteristics of the PFA, and without causing any contaminationproblem due to leaching. The melt formabletetrafluoroethylene/fluoroalkoxy trifluoroethylene copolymer compositionof this invention is characterized by containing apolytetrafluoroethylene having a crystallization temperature of at least305° C. and a heat of crystallization of at least 50 J/g.

DETAILED DESCRIPTION OF THE INVENTION

The composition of this invention generates fine spherulites, therebygiving melt extruded articles such as bottles and tubes which have farsuperior surface smoothness compared to molded articles fromconventional PFA. Consequently, the extent of adhering contaminants isreduced. Finer spherulites result in superior visual image resolutionwhen one looks through these molded articles. The PTFE used as anadditive has heat resistance and chemical resistance properties as goodas those of PFA, so that there is no problem of contaminatingsemiconductor fabrication steps due to leaching. In addition, thecompositions of this invention maintain melt moldability and mechanicalproperties equivalent to those of conventional PFA.

As will be seen in Examples and Comparative Examples given later, thereis a correlation between the surface roughness of a molded product andthe average spherulite diameter (hereafter "recrystallized averagespherulite diameter") obtained by melting the molded article (part ofthe molded article being cut out to be used as the test piece), followedby cooling the melt at a cooling rate of 10° C./min forrecrystallization or the maximum spherulite diameter (hereafter"recrystallized maximum spherulite diameter"), so that under the samemolding conditions, the smaller the recrystallized average spherulitediameter (or the recrystallized maximum spherulite diameter), thesmoother the surface of the molded article. The expressions"recrystallized average spherulite diameter" and the "recrystallizedmaximum spherulite diameter" are defined later herein. In general, amelt extruded product of a PFA composition which is generally availableon the market having a recrystallized average spherulite diameter of 55μm (70 μm for the recrystallized maximum spherulite diameter) has arough surface. However, the melt molded articles obtained from thecomposition of this invention having a recrystallized average spherulitediameter of 3 μm (5 μm for the recrystallized maximum spherulitediameter) show little surface roughness. The molded articles obtainedfrom the composition of this invention, which have recrystallizedaverage spherulite diameters of not more than 15 μm, preferably not morethan 10 μm, thereby provide a smooth surface.

The term tetrafluoroethylene/fluoroalkoxy trifluoroethylene copolymer(PFA) referred to in this invention means crystalline copolymers oftetrafluoroethylene and at least one fluoroalkoxy trifluoroethylenerepresented by Formula 1 or Formula 2, with fluoroalkoxytrifluoroethylene content in the copolymer being 1-10 wt % based ontotal copolymer. The copolymer is melt formable by melt extrusion,injection molding, or the like, and has a melt flow rate (MFR) of0.5-500 g/10 min, preferably 0.5-50 g/10 min at 372° C.±1° C. Thefluoroalkoxy trifluoroethylenes of formula 1 and 2 includeperfluoro(methyl vinyl ether), perfluoro(propyl vinyl ether),perfluoro(isobutyl vinyl ether), and the like. ##STR1## wherein X is Hor F, n is an integer of 0-4 and m is an integer of 0-7. ##STR2##wherein q is an integer of 0-3

The polytetrafluoroethylene (PTFE) that is incorporated into the PFA inthis invention is a homopolymer of tetrafluoroethylene (TFE) or amodified PTFE containing not more than 1 wt % of a modifying comonomer,such as hexafluoropropylene (HFP), fluoroalkoxy trifluoroethylene,fluoroalkyl ethylene, chlorotrifluoroethylene, or the like. The PTFEmust have a crystallization temperature of at least 305° C. and a heatof crystallization of at least 50 J/g, as measured with a differentialscanning calorimeter (DSC) by a method which will be described later.

There is a correlation between the crystallization temperature of thePTFE incorporated in a PFA and the effect of rendering finerspherulites: the higher the crystallization temperature, the smaller theamount needed for rendering finer spherulites. The PTFE must have acrystallization temperature of at least 305° C., preferably at least310° C., more preferably 312° C.

A PTFE having a heat of crystallization of at least 50 J/g is requiredto obtain the effect of fine spherulites under conditions in which highshear of the PFA composition is involved, as by the revolution of screwswhen melt mixing or extruding the composition.

The crystallization temperature and heat of crystallization of PTFE areknown to depend upon two factors: the modifier content and the molecularweight. For example, standard specific gravity (SSG) is ordinarilydetermined as an indirect measure of molecular weight for high molecularweight PTFE, SSG being a parameter that increases with decreasingmolecular weight. The general relationship between SSG and numberaverage molecular weight is well known. See, for example, Sperati &Starkweather, Fortschr. Hochpolym.-Forsch. 2, 465(1961). Higher specificgravity corresponds to higher crystallinity which is accompanied, ofcourse, by higher heat of crystallization. On the other hand, ifmolecular weight is too low or modifier content is too high, thencrystallization temperature is reduced below 305° C. In contrast to aPTFE "molding powder" which is molded by compressionpremolding/sintering, or a PTFE "fine powder", molded by pasteextrusion/sintering, all of which have number average molecular weightsof several million or higher and heats of crystallization typically of20-35 J/g and crystallization temperatures typically of 305° C.-315° C.,the PTFE which is suitable for the objective of this invention has alower molecular weight and a higher crystallinity. This type of PTFE canbe obtained by selecting conditions with consideration of the above twofactors in the known manufacturing processes for low molecular weightPTFE's, such as the polymerization of TFE in the presence of a chaintransfer agent or the thermal decomposition or radiation degradation ofa "molding powder" or a "fine powder" or a molded article therefore.Such PTFE is low in molecular weight and highly crystalline, andconsequently has high heat of crystallization. Thus, it lacks mechanicalstrength and cannot be used by itself for molding, unlike "moldingpowder" or "fine powder". However, low molecular weight PTFE was foundto have no adverse effect on the mechanical properties of a PFA whenused in small amounts for achieving the surface smoothening objective ofthis invention. Low molecular weight PTFE prepared by subjecting highermolecular weight PTFE to ionizing radiation is a preferred PTFE for usein the compositions of this invention.

Incorporating a PTFE which satisfies the above conditions in a PFA willrapidly decrease the recrystallized average spherulite diameter. Withrespect to the lower limit for the content, it is difficult to give anumerical limitation because a smaller content can still give a finespherulite if the PTFE which is incorporated has a highercrystallization temperature, but the preferred content is the effectiveamount which is able to provide a recrystallized average spherulitediameter for the PFA composition of not more than 15 μm, preferably notmore than 10 μm, when the composition is allowed to crystallize from themelt at a cooling rate of 10° C./min. As will be described later inTable 4, incorporating 0.01 wt % of a PTFE having a crystallizationtemperature, Tc, of 314° C. and a heat of crystallization, Hc, of 60 J/ggives a recrystallized average spherulite diameter of 13 μm, so that themeasure for the lower limit of the PTFE content would be about 0.01 wt%.

In order to improve the surface smoothness of the molded articles, therecrystallized average spherulite diameter is preferably made as smallas possible. In general, increasing the PTFE content tends to decreasethe recrystallized average spherulite diameter, but as the contentreaches 1-2 wt % or more, the further extent of reduction in therecrystallized average spherulite diameter with an increase in thecontent becomes smaller; as the PTFE content exceeds about 20 wt %, therecrystallized average spherulite diameter begins to plateau, resultingin the surface smoothness also becoming constant, so that the upperlimit for the amount of PTFE added is not definitive. With an increasein the PTFE content, the composition tends to be higher incrystallinity, without any adverse affect to the mechanical properties,such as tensile strength or folding endurance, etc., as long as the PTFEcontent is 2-4 wt % or less, although this depends upon the MFR valuesof PFA's. However, incorporation beyond these levels begins to graduallydecrease the physical properties, so that levels exceeding about 50 wt %of PTFE will drastically decrease the mechanical properties; therefore,the upper limit of addition of the PTFE is preferably 50 wt % or less,more preferably 30 wt % or less, and even more preferably, 4 wt % orless. PTFE content is based on combined weight of PTFE and PFA in thecomposition.

The methods used for adding and blending PTFE with PFA in this inventioninclude any method known in the art, such as melt blending, dry blendingPFA pellets or powder with a PTFE powder, wet blending a PFA liquiddispersion with a PTFE powder or PTFE liquid dispersion, or the like. Itis also possible to use a method by which PTFE particles are dispersedin a polymerization medium of the polymerization kettle for PFA in apreliminary step, followed by initiating the polymerization of PFA,thereby generating a PFA composition containing PTFE. Since the PTFEused in this invention is extremely compatible with the PFA in themelted state, it is easily dispersed in the PFA during melt blending ormelt extrusion, thereby providing an extremely homogeneous composition.That is, the PTFE particles are no longer distinguishable from the PFAmatrix when a sample prepared as for measurement of spherulite diameteris examined under an optical microscope at 100× magnification, or by DSCanalysis. Therefore, there is no particular limitation as to theconfiguration of the PTFE being added, normally in terms of workability,a dispersion of fine particles with average particle sizes of 0.05-1 μmor several μm to several tens of μm is used.

EXAMPLES

The present invention is specifically described by the followingExamples and Comparative Examples. Atetrafluoroethylene/perfluoro(propyl vinyl ether) (PPVE) copolymer wasused as the tetrafluoroethylene/fluoroalkoxy trifluoroethylene copolymer(PFA), for which the following methods were used to measure the PPVEcontent, melt flow rate (MFR), melt temperature, crystallizationtemperature, heat of crystallization, maximum spherulite diameter,tensile strength, elongation, and MIT folding endurance.

PPVE Content: A PFA sample was compressed at 350° C. and water cooled togive a 50 μm thick film, which was used to measure the infraredabsorption spectrum (in a nitrogen atmosphere) from which an absorbanceratio was obtained according to Equation 3. The sample PPVE content wasdetermined by comparing the ratio with a calibration curve obtainedpreliminarily with standard films containing known PPVE contents.##EQU1##

Melt Flow Rate (MFR): This was measured on a Toyo Seiki Company MeltIndexer by holding a 5 g sample in an 9.53 mm inside diameter cylinderat 372° C.±1° C. for 5 minutes and then extruding it under a 5 kg weight(piston and weight) through an orifice 2.1 mm in diameter and 8 mm long,thereby measuring the rate of extrusion (g/10 min) which was reported asMFR.

Melt Temperature, Crystallization Temperature, and Heat ofCrystallization: A Perkin Elmer differential scanning calorimeter DSCModel 7 was used. A 5 mg sample was weighed in a dedicated aluminum pan,crimped by a crimper, placed in the DSC proper, and heating was started.The heating was at a rate of 10° C./min from 200° C. to 380° C. The meltpeak temperature was read from a melting curve as melt temperature Tm-1.After the sample was held for one minute at 380° C. the sample wascooled at a rate of 10° C./min to 200° C. to obtain a crystallizationcurve, from which a crystallization peak temperature was obtained as thetemperature of crystallization (Tc). The heat of crystallization (Hc)was obtained according to the usual procedure from the peak area definedby connecting with a straight line the point at which the curve departsfrom the baseline near the crystallization peak and the point at whichthe curve returns back to the baseline. After the sample was held forone minute at 200° C., the sample was then heated again to 380° C. at arate of 10° C./min to give a melt curve from which the melt peaktemperature was taken as melt temperature Tm-2. Each numerical value wasobtained to one decimal point and was rounded by the method of JISZ8401.

Recrystallized Average Spherulite Diameter: Melt indexer extrudate fromMFR measurement was sliced in a radial direction to give a disc about0.2 mm thick as a sample. The disc was placed on a slide glass and theslide glass was mounted on a Metier FP82HT model hot stage. The samplewas melted by heating at a rate of 40° C./min to 360° C., followed byholding for 3 minutes at 360° C. and then cooling to 200° C. at a rateof 10° C./min for recrystallization. After reaching the sampletemperature of 200° C., the slide glass holding the sample was removedfrom the hot stage and the sample surface was observed with an opticalmicroscope at magnifications of 100× and 400×. The spherulite structurewas confirmed by polarized light. Diameters of 200 contiguousspherulites observed on the sample surface were measured to obtain anaverage value which was defined as "the recrystallized averagespherulite diameter". The maximum diameter for contiguous spheruliteswas defined as "the recrystallized maximum spherulite diameter". Sincespherulites were observed as polyhedra distorted by collision withadjacent spherulites, their major axes were reported as their diameters.Spherulite diameters were also measured with a scanning electronmicroscope (at magnifications of 3000× and 5000×) for samples havingrecrystallized average spherulite diameters of 5 μm or less.

Tensile Strength and Elongation: The sample was filled into a mold whichhad been heated to 350° C. on a hot press, heated 20 minutes, pressedabout 1 minute under a pressure of about 5 kgf/cm², followed by movingthe mold to a press at room temperature and pressing under a pressure ofabout 30 kgf/cm², and allowing it to cool for 20 minutes. The resultantsheet was about 1.5 mm thick and was cut out to give about five testpieces according to ASTM D1457-83 so as to carry out a tensile test withan initial grip distance of 22.2 mm at a separation rate of 50 mm/min tomeasure the strength at the break and elongation at the break (theaverage values from five test pieces).

MIT Folding Endurance: The sample was heated for 15 minutes in a moldheated to 350° C. on a hot press and pressed for about 1-4 minutes at apressure of 30-60 kgf/cm², the pressure being different depending uponthe MFR of the PFA, followed by moving the mold to a press at roomtemperature to be pressed at about 50 kgf/cm², followed by standing for15 minutes and cooling. The resultant 0.19-0.21 mm thick film was cutout to give test pieces about 110 mm long and 15 mm wide; the testpieces therefrom were mounted on a Toyo Seiki K.K. MIT Folding EnduranceMachine according to the specification of ASTM-2176 so as to fold undera load of 1 kg from left and right to an angle of 135° at a rate of 175cycles/minute. The number of oscillating folds made until the testpieces ruptured (the average from three test pieces) was defined as theMIT folding endurance.

Examples 1-6 and Control Examples 1-3

Ninety-nine parts by weight of PFA melt extruded pellets having a PPVEcontent of 3.0 wt %, an MFR of 2.0 g/10 min, a recrystallized averagespherulite diameter of 44 microns, and a recrystallized maximumspherulite diameter of 68 microns, and 1 part by weight of a PTFE powder(average particle size of 2-20 μm) from eight types A-H having theproperties shown in Table 1 were fed into a roller mixer (Toyo SeikiK.K., R-60 Model; mixer volume about 60 cm³ ; material of constructionfor the mixing pan: Hastelloy® C-276) so as to melt mix for 10 minutesat a mixing section set temperature of 350° C., a resin temperature of345°-352° C. and the rate of roller revolutions at 15 rpm to give a PFAcomposition containing 1 wt % PTFE. PTFE types B, E and F arecommercially available powders, respectively, TLP 10F-1 (Mitsui DuPontFluorochemicals), MP-1200 (DuPont), and L-5 (Daikin). PTFE types A, C, Dand G were prepared from various PTFE "molding powder" and "fine powder"by gamma irradiation with doses in the range 1-20 Mrad. PTFE type H wasprepared by thermal degradation of a melt formable copolymer. PTFE typesA and H did not satisfy the heat of crystallization or crystallizationtemperature requirement of this invention. For the purpose ofcomparison, the above-described PFA alone with no PTFE was also meltmixed under the same conditions (Control Example 1). Each compositionwas then cut into 3-5 μm square pellets after melt mixing to obtainsamples for molding. Table 2 shows the properties of each of thesecompositions and test pieces molded from these compositions.

                                      TABLE 1                                     __________________________________________________________________________    PTFE Types Used                                                                       A   B  C  D   E  F   G   H                                            __________________________________________________________________________    Modifier Type                                                                         None                                                                              HFP                                                                              HFP                                                                              None                                                                              HFP                                                                              NOne                                                                              PPVE                                                                              PPVE                                         Content     0.1                                                                              0.05   0.1    0.1 1.2                                          (wt %)                                                                        DSC Analysis of PTFE:                                                         Tm-1 (°C.)                                                                     332 330                                                                              329                                                                              332 322                                                                              326 331 320                                          Tm-2 (°C.)                                                                     327 327                                                                              329                                                                              328 324                                                                              328 328 320                                          Tc (°C.)                                                                       314 315                                                                              312                                                                              316 312                                                                              308 313 302                                          Hc (J/g)                                                                              43  60 61 58  59 67  53  57                                           __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________    Results for Examples 1-6 and Controls 1-3                                              Control                                                                       Examples Examples                                                    Nos.     1  2  3  1   2  3  4  5  6                                           __________________________________________________________________________    PTFE Type                                                                              -- A  H  B   C  D  E  F  G                                           PTFE (wt %)                                                                            0  1  1  1   1  1  1  1  1                                           Composition:                                                                  MFR (g/10 min)                                                                         1.9                                                                              1.8                                                                              2.0                                                                              1.9 2.0                                                                              1.9                                                                              1.9                                                                              1.9                                                                              1.9                                         Tm-2 (°C.)                                                                      307                                                                              308                                                                              308                                                                              308 308                                                                              309                                                                              308                                                                              308                                                                              309                                         Test Piece:                                                                   RASD.sup.a (μm)                                                                     29 26 24 3   5  2  7  12 4                                           RMSD.sup.b (μm)                                                                     45 40 35 5   7  4  11 18 7                                           __________________________________________________________________________     .sup.a Recrystallized Average Spherulite Diameter                             .sup.b Recrystallized Maximum Spherulite Diameter                        

In contrast to a composition having no PTFE in PFA (Control Example 1),a composition having PTFE A with a heat of crystallization less than 50J/g (Control Example 2), and a composition having a PTFE H with acrystallization temperature below 305° C. (Control Example 3), which allhad recrystallized average spherulite diameters of the melt-formedproducts of 24 μm or greater (a recrystallized maximum spherulitediameter of 35 μm or greater), compositions from Examples 1-6 containing1 wt % of PTFE B-G having a crystallization temperature of at least 305°C. (Tc) and a heat of crystallization (Hc) of at least 50 J/g, all hadrecrystallized average spherulite diameters of 15 μm or less andrecrystallized maximum spherulite diameters of 20 μm or less in themelt-formed products. A comparison of Examples 1, 3, and 5 shows thatExample 3 which contains PTFE D having the highest Tc at 316° C. had thesmallest recrystallized average spherulite diameter at 2 μm, followed byExample 1 containing a PTFE B having a Tc of 314° C. and arecrystallized average spherulite diameter of 3 μm (a recrystallizedmaximum spherulite diameter of 5 μm); and Example 5 containing PTFE Fhaving the lowest Tc of 308° C. had a recrystallized average spherulitediameter of 12 μm and recrystallized maximum spherelite diameter of 18μm, the largest among the Examples of this invention.

Control Example 4

An aqueous PTFE dispersion containing PTFE with an average particle sizeof about 0.2 μm which on coagulation would give a fine powder with aTm-1 of 337° C., a Tm-2 of 327° C., a Tc of 314° C., and an Hc of 34J/g, was added to an aqueous dispersion of a PFA with an averageparticle size of about 0.2 μm, a PPVE content of 3.0 wt %, a Tm-2 of309° C. so as to reach a weight ratio of PFA resin and PTFE resin of99:1. The dispersion mixture was coagulated by stirring and addingnitric acid to destroy the emulsion followed by addingtrichlorotrifluoroethane and stirring to form granules. The resultantgranular powder was water washed, dried, and heat treated for 15 hoursat 290° C. to obtain a powdery composition having an average particlesize of about 450 μm. The composition had an MFR of 1.7 g/10 min givinga melt indexer extruded product having a recrystallized averagespherulite diameter of 2 μm and a recrystallized maximum spherulitediameter of 3 μm. However, when this powder composition was fed into aroller mixer and melt mixed in a manner similar to that of Example 1,the melt mixed product had an MFR of 1.7 g/10 min and a melt indexerextrudate having a recrystallized average spherulite diameter of 33 μmand a recrystallized maximum spherulite diameter of 45 μm. Incidentally,a PFA powder obtained in a similar manner, except for not adding anyPTFE had an MFR of 2.4 g/10 min and a recrystallized average spherulitediameter of 56 μm, and a recrystallized maximum spherulite diameter of70 μm, which after melt mixing gave an MFR of 2.3 g/10 min with a meltindexer extrudate having a recrystallized average spherulite diameter of35 μm and a recrystallized maximum spherulite diameter of 45 μm. Theabove results show that a PFA powder to which a PTFE from the ControlExample having a heat of crystallization of 34 J/g was added gives anextrudate having the extremely small values of recrystallized averagespherulite diameter of 2 μm and a recrystallized maximum spherulitediameter of 3 μm. However these results indicate that, when thiscomposition is mixed during melting under shear force, the effect ofrendering finer spherulites is lost.

Example 7

PFA melt extruded pellets of a PPVE content of 3.0 wt %, an MFR of 1.9g/10 min, and a recrystallized average spherulite diameter of 55 μm anda recrystallized maximum spherulite diameter of 77 μm, and the PTFEpowder B (Tc=314° C., Hc=60 J/g) used in Example 1, were melt mixed atthe mixing ratios given in Table 3 in a manner similar to that ofExample 1. Table 3 shows the properties of the resultant compositionsand test pieces molded from the compositions. This example used apressure of 60 kgf/cm² for about 4 minutes for pressing before the moldwas moved to a room temperature press in the preparation of test piecesfor the MIT folding endurance test.

                                      TABLE 3                                     __________________________________________________________________________    Effect of PTFE Concentration, Example 7                                       PTFE B (wt %)                                                                           0  0.1                                                                              0.2                                                                              0.5                                                                              1  2  3  4  5  10 20 50                                 __________________________________________________________________________    Composition:                                                                  MFR (g/10 min)                                                                          1.7                                                                              1.7                                                                              1.7                                                                              1.7                                                                              1.7                                                                              1.7                                                                              1.7                                                                              1.7                                                                              1.7                                                                              1.5                                                                              1.4                                                                              1.2                                Tm-2 (°C.)                                                                       308                                                                              309                                                                              309                                                                              309                                                                              310                                                                              310                                                                              310                                                                              312                                                                              312                                                                              314                                                                              318                                                                              324                                Tc (°C.)                                                                         282                                                                              286                                                                              288                                                                              289                                                                              289                                                                              290                                                                              290                                                                              292                                                                              293                                                                              295                                                                              299                                                                              306                                Hc (J/g)  23 23 23 22 23 24 23 25 25 26 28 33                                 Test Pieces (Molded Article)                                                  RASC.sup.a (μm)                                                                      44 13 8  5  4  3  3  3  3  1  2  2                                  RMSD.sup.b (μm)                                                                      6  20 13 8  5  4  5  4  4  3  3  3                                  Tensile Strength                                                                        353                                                                              353                                                                              359                                                                              358                                                                              353                                                                              342                                                                              355                                                                              337                                                                              328                                                                              326                                                                              320                                                                              189                                (kfg/cm.sup.2)                                                                Elongation at                                                                           376                                                                              368                                                                              378                                                                              380                                                                              375                                                                              366                                                                              378                                                                              360                                                                              347                                                                              360                                                                              378                                                                              268                                Break (%)                                                                     Folding Endurance                                                                       9.4                                                                              14 9.3                                                                              14 12 13 13 12 8.3                                                                              8.0                                                                              5.8                                                                              0.11                               __________________________________________________________________________     .sup.a Recrystallized average spherulite diameter                             .sup.b Recrystallized mamimum spherulite diameter                        

Table 3 shows that a PTFE content as small as 0.1 wt % drasticallyreduces the recrystallized average spherulite diameter from 44 μm withno PTFE to 13 μm, and recrystallized average maximum spherulitediameters from 63 μm with no PTFE to 20 μm with PTFE; 1 wt %incorporation gives a recrystallized average spherulite diameter of 4 μmand an average maximum spherulite diameter of 5 μm; 2 wt % PTFE contentgives a reduction down to a recrystallized average spherulite diameterof 3 μm and a recrystallized maximum spherulite diameter of 4 μm.However, incorporating more than 2 wt % PTFE causes little furtherdecrease of the recrystallized average spherulite diameter or therecrystallized maximum spherulite diameter. The Table also shows that aPTFE content of not more than 4 wt % gives no appreciable adverseeffects on the tensile strength, elongation, or folding endurance tests.[0035]

Example 8

Melt extruded pellets of PFA having a PPVE content of 3.4 wt %, an MFRof 15.0 g/10 min, and a recrystallized average spherulite diameter of 49μm and a recrystallized maximum spherulite diameter of 62 μm were meltmixed in a manner similar to that of Example 1 at the contents given inTable 4 using PTFE powder B (Table 1). Table 4 shows the properties ofthe resultant compositions and the test pieces molded from thecompositions. In this Example, the molding conditions were a pressure of30 kgf/cm² for about one minute before the mold was moved to a press atroom temperature in preparing test pieces for the MIT folding endurancetest.

                                      TABLE 4                                     __________________________________________________________________________    Effect of PTFE Concentration, Example 8                                       PTFE B (wt %)                                                                           0  0.01                                                                             0.1                                                                              0.2                                                                              0.5                                                                              1  2  3  5  10 20 50                                 __________________________________________________________________________    Composition:                                                                  MFR (g/10 min)                                                                          14.8                                                                             14.8                                                                             14.8                                                                             14.8                                                                             14.9                                                                             14.9                                                                             14.4                                                                             13.9                                                                             13.0                                                                             12.0                                                                             9.8                                                                              2.3                                Tm-2 (°C.)                                                                       308                                                                              308                                                                              308                                                                              309                                                                              309                                                                              309                                                                              312                                                                              312                                                                              314                                                                              318                                                                              320                                                                              326                                Tc (°C.)                                                                         283                                                                              286                                                                              288                                                                              289                                                                              289                                                                              290                                                                              294                                                                              294                                                                              296                                                                              300                                                                              303                                                                              311                                Hc (J/g)  25 25 25 26 29 29 28 31 30 30 32 36                                 Test Pieces (Molded Article)                                                  RASC.sup.a (μm)                                                                      38 13 5  5  4  3  3  3  3  2  2  2                                  RMSD.sup.b (μm)                                                                      50 18 8  8  6  5  4  4  5  3  3  3                                  Tensile Strength                                                                        308                                                                              321                                                                              304                                                                              308                                                                              285                                                                              297                                                                              289                                                                              273                                                                              284                                                                              254                                                                              231                                                                              149                                (kgf/cm.sup.2)                                                                Elongation at                                                                           432                                                                              443                                                                              422                                                                              448                                                                              411                                                                              432                                                                              423                                                                              397                                                                              425                                                                              388                                                                              357                                                                              59                                 Folding Endurance                                                                       2.3                                                                              2.8                                                                              2.5                                                                              2.0                                                                              1.9                                                                              2.0                                                                              1.4                                                                              1.4                                                                              1.4                                                                              1.0                                                                              -- --                                 __________________________________________________________________________     .sup.a Recrystallized average spherulite diameter                             .sup.b Recrystallized maximum spherulite diameter                        

Table 4 shows that a PTFE content at a level of only 0.01 wt %drastically decreases the recrystallized average spherulite diameterfrom 38 μm with no PTFE to 13 μm, and the recrystallized maximumspherulite diameter from 50 μm with no PTFE down to 18 μm; incorporating1 wt % weight reduces the recrystallized average spherulite diameterdown to 3 μm and the recrystallized maximum spherulite diameter to 5 μm;a 2 wt % PTFE incorporation reduces the recrystallized averagespherulite diameter to 3 μm and the recrystallized maximum spherulitediameter to 4 μm. However, incorporating more than 2 wt % PTFE haslittle further effect on the spherulite diameter.

Example 9

The PFA pellets used in Example 8 and the PTFE powder E used in Example4 were melt mixed at the mixing contents given in Table 5 in a mannersimilar to that of Example 1. Table 5 shows the properties of theresultant compositions and the test pieces molded from thesecompositions. Trends similar to those of Examples 7 and 8 are observed.In this Example, the molding press conditions were a pressure of 30kgf/cm² for about one minute before the mold was moved to a press atroom temperature in preparation of test pieces for the MIT foldingendurance test.

                  TABLE 5                                                         ______________________________________                                        Effect of PTFE Concentration, Example 9                                       PTFE B (wt %)                                                                             0      0.5    1    2    3    4    5                               ______________________________________                                        Composition:                                                                  MFR (g/10 min)                                                                            14.8   15.3   15.3 15.6 15.8 16.1 16.3                            Tm-2 (°C.)                                                                         308    308    308  309  310  310  310                             Tc (°C.)                                                                           283    287    288  289  289  290  291                             Hc (J/g)    25     25     25   25   25   26   26                              Test Pieces (molded article):                                                 RASC.sup.a (μm)                                                                        38     7      6    5    5    4    4                               RMSD.sup.b (μm)                                                                        50     10     8    8    7    5    5                               Folding Endurance                                                                         2.3    2.2    1.8  1.7  1.5  1.3  1.1                             (10.sup.4 Cycles)                                                             ______________________________________                                         .sup.a Recrystallized average spherulite diameter                             .sup.b Recrystallized maximum spherulite diameter                        

Control Example 5

PFA pellets used in Example 7 and PTFE powder H used in Control Example3 were melt mixed in a manner similar to that of Example 1 except forthe levels of contents as given in Table 6. Table 6 shows the resultantcompositions and properties of the test pieces molded from thosecompositions. Even when the content was increased to 10 wt %, therecrystallized average spherulite diameter was 21 μm and therecrystallized maximum spherulite diameter was 30 μm or greater.

                  TABLE 6                                                         ______________________________________                                        Results for Control Example 5                                                 PTFE H (wt %)       0     2       5   10                                      ______________________________________                                        Composition: MFR (g/10 min)                                                                       1.7   1.9     2.1 2.4                                     Test Piece: RASD.sup.a (μm)                                                                    44    35      24  21                                      Test Piece: RMSD.sup.b (μm)                                                                    63    50      30  30                                      ______________________________________                                         .sup.a Recystallized average spherulite diameter                              .sup.b Recrystallized maximum spherulite diameter                        

Example 10

A coagulated powder was obtained by stirring an aqueous dispersion of aPFA (average particle size of about 0.2 μm, PPVE content of 3.1 wt %,melt temperature of 308° C.), adding nitric acid and thentrichlorotrifluoroethane, and drying for 10 hours at 150° C. Theresultant dried powder (995 parts by weight) and 5 parts by weight ofPTFE powder B used in Example 1 were fed into a Henschel mixer (MitsuiMiikekakoki Company: FM10B Model) for mixing for 10 minutes at 3000 rpm,followed by adding, while decreasing the number of revolutions to 1000rpm, 150 parts by weight of pure water and then 500 parts by weight oftrichlorotrifluoroethane in small increments, followed by increasing thenumber of revolutions to 3000 rpm and stirring for one minute to obtaina granulated powder. This powder was then heat treated for 12 hours at300° C. to obtain a powder composition having an average particle sizeof about 380 μm. The composition had an MFR of 0.6 g/10 minutes and amelt indexer extrudate having a recrystallized average spherulitediameter of 3 μm and a recrystallized maximum spherulite diameter of 5μm. A PFA powder obtained by a similar operation using no addition ofPTFE had an MFR of 0.6 g/10 minutes with a recrystallized averagespherulite diameter of 55 μm and a recrystallized maximum spherulite adiameter for the extrudate of 70 μm.

Example 11

The powder composition obtained in Example 10 and a PFA powder were usedto mold tubes having outside diameter of 12.2 mm and wall thickness of1.0 mm under the following conditions:

Extruder (Tanabe Plastics Kikai Company)

Cylinder inside diameter: 30 mm (L/D 20)

Die inside diameter: 25 mm

Mandrel diameter: 17 mm

Set Temperatures (°C.):

Cylinder Rear Section: 300

Cylinder Center 360

Cylinder Front: 380

Adapter 380

Crosshead: 380

Die: 400-430

Screw Revolutions: 10 rpm

Sizing Die inside diameter: 12.5 mm

Take-Up Rate: 0.5 m/min

A sample of about 5 mm square was cut out from the tube to measure thesurface roughness of the tube inside by a stylus probe-typethree-dimensional surface roughness measurement device (Tokyo SeimitsuCompany SURFCOM 575A-3DF) to give the results shown in Table 7. A testpiece cut out from a tube gave a melt index extrudate having the samemeasured recrystallized average spherulite diameter as that of thecomposition of Example 10. 0.5% by weight of PTFE. Table 7 clearly showsthat the inside surface of a tube prepared from a composition containing0.5% by weight of PTFE and having a recrystallized average spherulitediameter of 3 μm and a recrystallized maximum spherulite diameter of 5μm had far superior surface smoothness compared to the inside of a tubemolded from a PFA powder containing no PTFE and having a recrystallizedaverage spherulite diameter of 55 μm and a recrystallized maximumspherulite diameter of 70 μm.

                                      TABLE 7                                     __________________________________________________________________________    Results for Example 11                                                                 Recrystallized                                                                            Surface Roughness of the Inside                                   Spherulite Diameters                                                                      of the Tubes                                                                  Centerline Average                                                                      Maximum                                        Amount of PTFE                                                                         Average                                                                             Maximum                                                                             Roughness (Ra)                                                                          Height (Rt)                                    Added (wt %)                                                                           (μm)                                                                             (μm)                                                                             (μm)   (μm)                                        __________________________________________________________________________    No Additive                                                                            55    70    0.10      0.64                                           0.5      3     5     0.02      0.10                                           __________________________________________________________________________

Example 12

A PFA powder having PPVE content of 3.0 wt %, MFR of 1.9 g/10 min, andaverage particle size of about 500 μm (995 parts by weight) and 5 partsby weight of PTFE powder D used in Example 3 were fed to the screwextruder and melt mixed and extruded at a resin temperature of 360° C.,followed by cutting the extrudate to give a pelletized compositionhaving an average particle size of about 3 mm. The composition had anMFR of 1.9 g/10 min, and the melt indexer extrudate had a recrystallizedaverage spherulite diameter of 3 μm and a recrystallized maximumspherulite diameter of 4 μm. PFA pellets, prepared according to the sameoperation except for adding no PTFE, gave an MFR of 1.9 g/10 min and themelt index extrudate gave a recrystallized average spherulite diameterof 66 μm and a recrystallized maximum spherulite diameter of 90 μm. Thecomposition and the PFA pellets were fed to a blow molding machine andextruded at a resin temperature of 390° C. to give 1 L volume bottles,having an outside diameter of 90 mm and a wall thickness of about 1 mm.About a 5 mm square sample was cut out from the bottle and the inside ofthe bottle was measured for its surface roughness with a scanning lasermicroscope (Laser Tech TCH K.K., Model ILM21) giving the results shownin Table 8. The melt index extrudates from the test pieces cut out fromthese bottles gave recrystallized average spherulite diameters andrecrystallized maximum spherulite diameters which were measured to besame as those of the above compositions. Table 8 clearly shows that theinside of the bottle molded from the PFA composition containing 0.5% byweight of PTFE and having a recrystallized average spherulite diameterof 3 μm and recrystallized maximum spherulite diameter of 4 μm is farsuperior in surface smoothness to that of the inside of the bottlemolded from PFA powder having no PTFE added and having a recrystallizedaverage spherulite diameter of 66 μm and a recrystallized maximumspherulite diameter of 19 μm.

                                      TABLE 8                                     __________________________________________________________________________    Results for Example 12                                                                 Recrystallized                                                                            Surface Roughness of the Inside                                   Spherulite Diameters                                                                      of the Bottles                                                                Centerline Average                                                                      Maximum                                        Amount of PTFE                                                                         Average                                                                             Maximum                                                                             Roughness (ra)                                                                          Height (Rt)                                    Added (wt %)                                                                           (μm)                                                                             (μm)                                                                             (μm)   (μm)                                        __________________________________________________________________________    No Additive                                                                            66    90    0.60      8.96                                           0.5      3     4     0.09      1.15                                           __________________________________________________________________________

What is claimed is:
 1. An article melt-formed from crystallinetetrafluoroethylene/fluoroalkoxy trifluoroethylene copolymer whichcontains polytetrafluoroethylene having a crystallization temperature ofat least 305° C. and heat of crystallization of at least 50 J/g, whereinthe resultant composition has recrystallized average spherulite diameterof not more than 15 micrometers, said article being a bottle.
 2. Anarticle as set forth in claim 1 in which the amount of thepolytetrafluoroethylene contained in thetetrafluoroethylene/fluoroalkoxy trifluoroethylene copolymer compositionis not more than 50% by weight.
 3. An article melt-formed fromcrystalline tetrafluoroethylene/fluoroalkoxy trifluoroethylene copolymerwhich contains polytetrafluoroethylene having a crystallizationtemperature of at least 305° C. and heat of crystallization of at least50 J/g, wherein the resultant composition has recrystallized averagespherulite diameter of not more than 15 micrometers, said article beinga tube for the transport of liquid.